What is subsistence agriculture, and why does it often result in poverty?

I would say Subsistence farming, or subsistence agriculture, is a mode of agriculture in which a plot of land produces only enough food to feed the family or small community working it. All produce grown is intended for consumption purposes as opposed to market sale or trade.

when the chinese communist party took power in 1949, it began to build new di and levees to hold the yellow and yangtze rivers back.